This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-67315 filed Mar. 9, 2001.
The present invention relates to a failure detection method and apparatus for a sensor network where a plurality of pressure sensitive sensors are connected in a matrix.
In a passenger detection sensor network for a vehicle, condition of wiring that connects each pressure sensitive sensor to an electronic control unit (ECU) needs to be monitored for a proper passenger detection operation. One proposed method for monitoring the matrix sensor network is shown in FIG. 7. A line 120 for monitoring row lines 100 by the ECU is connected to each row line 100 (#1 to #3), and a resistor 130 is connected between each row line 100 and its corresponding line 120. For monitoring column lines 110 (#A to #C), lines 120 and resistors 130 are connected in the same manner as rows. As a result, series circuits are constructed so that operativeness of lines 100 and 110 is monitored by feeding a test current by the ECU.
However, to detect failures (open and/or short) in a matrix circuit that contains m rows and n columns, a number of lines as many as mxc3x972+nxc3x972 are required even though a plurality of pressure sensitive sensors is connected in a matrix to reduce wiring.
The present invention therefore has an objective to provide a failure detection method and apparatus for a sensor network requiring less wiring for a monitoring operation.
According to the present invention, a monitoring device such as a resistor is connected to ends of two row lines or two column lines to form a series circuit with a pull-up resistor. A voltage is applied to the series circuit to check operativeness of those lines based on the voltage or current variations in the series circuit. If no failure is present in the series circuit, the divided voltage corresponding to the ratio of the pull-up resistor and a sensor resistor is developed. If the series circuit is in the shorted condition, the voltage across the monitoring device is 0V. If the series circuit is in the open condition, the voltage is equal to the voltage applied to the series circuit.